Effects Of Zwitterionic Surfactants And Nanoparticles On The Performance Of Cyclic Olefin Copolymer Microchip Electrophoresis

Microfluidic chip electrophoresis(MCE)is a way for the miniaturization and integration of biological and chemical analysis systems,which can significantly reduce the analysis times and the consumption of reagents and samples and possess great application potential.The simplicity of the manufacturing technology and the variety of materials available for making microchips make the cost advantage of polymer microchips obvious.However,the surface of many polymers is hydrophobic,and the analytes or biological sample matrices are easily adsorbed on the microchip surface.As a result,the surface properties of the microchannels may change and homogeneity may become poor,which in turn leads to the widening of the analyte zone and reduces separation efficiency and analysis stability.Previous works have proved that neutral,anionic,and cationic polymers as additives can inhibit the adsorption of analytes on the surface of cyclic olefin copolymer(COC)microchips,and significantly improve the electrophoretic separation efficiency.In contrast to neutral additives,electrostatic interactions between additives with charged ionic groups and analytes facilitate improved electrophoretic separation selectivity.However,ionic additives increase solution conductivity and generate additional Joule heating during electrophoretic separation,which will exacerbate separation zone diffusion,affect buffer solution p H,viscosity,and chemical balance,and ultimately reduce separation efficiency and reproducibility.Therefore,the development of multi-functional additives with low conductivity and multiple interaction modes with analytes is helpful to expand the application range of polymeric microchip electrophoresis.In this thesis,zwitterionic surfactants were used as buffer additives to improve the separation efficiency,stability,and resolution of analytes with hydrophobic groups by COC MCE.An investigation of using low conductivity and amphiphilic nanoparticles as electrophoretic additives to tune the microchip electrophoretic behavior of analytes is also attempted to provide a fundamental reference for exploring efficient and lowcost MCE systems.The thesis contains five chapters:Chapter 1: The materials and methods for fabricating polymer microchips were described in detail.The methods for improving the electrophoretic separation performance of polymer microchip electrophoresis were also systematically summarized.Furthermore,the usage of zwitterionic surfactants and nanoparticles in improving capillary and microchip electrophoresis performance was elaborated.The problem of analyzing hydrophobic analytes with polymer microchip electrophoresis and its challenges in practical applications were discussed.The purpose and significance of the research in this thesis were proposed on this basis.Chapter 2: The surface adsorption of hydrophobic analytes renders their electrophoretic separation on COC microchips relatively difficult.For this reason,carboxybetaine 2-(dodecyldimethylammonio)acetate(DDAA)was used as an electrophoretic buffer additive and significantly improved the separation efficiency of the model analytes,hydrophobic benzophenanthridine alkaloids sanguinarine(SAN)and chelerythrine(CHE)with theoretical plate numbers of 3 × 105/m.The concentration of the organic solvent acetonitrile added to the running buffer was low(30%,v/v),and the electrophoretic separation time was short(50 s).The extra Joule heating originated from cationic DDAA with incomplete carboxyl group dissociation at low p H affected less the electrophoretic separation efficiency and reproducibility of SAN and CHE.In comparison with two sulfobetaines with different lengths of alkyl chains,the resolution of SAN and CHE with DDAA as an additive was relatively higher.In combination with laser induced fluorescence(LIF)detection,a method for rapid separation and detection of alkaloids was fabricated.The limits of detection(LODs,S/N = 3)for SAN and CHE were 1.0 nmol/L and 1.8 nmol/L,respectively.The established method was used to quantitatively determine SAN and CHE in Chelidonium majus,Weikening tablets,and honey,with standard addition recovery in the range of 98.2%–102.9%,indicating that the method is expected to be employed as a tool for quality control of relevant drugs and foods.Chapter 3: The cationic form of DDAA still generated additional Joule heating due to the incomplete dissociation of the carboxyl group of DDAA at low p H.Rhodamine dyes are easily adsorbed,and a higher content of organic solvents needs to be added to the running buffer solution for their separation and detection using COC microchip electrophoresis.Their separation efficiency and stability will be seriously affected if the Joule heating of the electrophoresis system is excessive.For the issue,a sulfobetaine that is nearly electroneutral over a wide range of p H,N-hexadecyl-N,N-dimethyl-3-ammonio-1-propane sulfonate(HDAPS),was selected as a buffer additive.Its effects on the electrophoretic separation of rhodamine dyes on COC microchip were investigated.In contrast to the ionic polymer poly(diallydimethylammonium chloride)(PDDA),HDAPS generated no additional Joule heating during the electrophoretic separation.The theoretical plate numbers for electrophoretic separation of four rhodamines reached 6.9 × 105/m with better reproducibility.In comparison with DDAA or sulfobetaine with a shorter alkyl chain,the separation efficiency and resolution of the four rhodamines were higher with HDAPS as an additive.Coupled with LIF assay for the separation and determination of rhodamine 123,rhodamine 6G,rhodamine B,and rhodamine 101 with LODs(S/N = 3)of 0.06–1.27 nmol/L.The method was applied to the detection of rhodamines in eyeshadow and wolfberry,with standard addition recovery of 98.2%–101.4%.Chapter 4: HDAPS,a buffer additive,exhibits a slow dissolution rate in aqueous solutions at room temperature,does not dissolve completely at higher concentrations,and the range of concentrations employed is not wide enough.Sulfobetaine,Ntetradecyl-N,N-dimethyl-3-ammonio-1-propane sulfonate(TDAPS),exhibits relatively favorable solubility in water at room temperature,and its dissolution rate still remains high at higher concentrations.In this work,TDAPS was used as an additive to improve the separation efficiency and stability of doxorubicin(DOX)and pirarubicin(PIR)by COC microchip electrophoresis.TDAPS did not generate Joule heating during the electrophoresis,and the electrophoretic separation of DOX and PIR was still highly reproducible,despite the organic solvent acetonitrile content of as high as 60%(v/v)in the running buffer solution.The electrophoretic separation performance of DOX and PIR when HDAPS and TDAPS were used as additives,respectively,was comparable,while the electrophoretic separation of two anthracyclines with DDAA as an additive exhibited a relatively weak signal.In combination with the LIF detection,a rapid(40 s)technique was developed for the separation and detection of anthracyclines using microchip electrophoresis.The LODs(S/N = 3)of DOX and PIR were 0.9 nmol/L and1.1 nmol/L,respectively.The method was applied to the analysis of anthracyclines in human blood samples,with standard addition recovery ranging from 95.6% to 101.3%,demonstrating the application potential of the proposed approach for the monitoring of anthracycline blood levels used in clinical treatment.Chapter 5: In order to further expand the variety of multifunctional additives,this work investigated the effects of nanoparticles with low electrical conductivity and capable of multiple interactions with analytes in combination with polymers as electrophoretic buffer additives on the electrophoretic separation of model analytes.Silica nanoparticles(SNPs)possessed high dispersion and suspension in phosphate buffer and borate buffer solutions.The fluorescent signal of the model analyte,rhodamine B isothiocyanate,was enhanced when it was compounded with PDDA as a buffer additive for COC microchip electrophoresis.The migration time of the model analyte fluorescein sodium(FS)increased,and the resolution of gabapentinoids labeled with fluorescein isothiocyanate was marginally improved when SNPs were complexed with hydroxypropyl cellulose(HPC)as an additive.Zeolitic imidazolate framework-8(ZIF-8)was dispersed stably in a phosphate buffer solution.The baseline fluctuation was slightly increased during electrophoretic separation of FS when ZIF-8 was combined with HPC or polyethylene oxide as an additive.When ZIF-8 was compounded with polyethyleneimine as an additive,the column efficiency was reduced and the migration time was prolonged for electrophoretic separation of FS in phosphate buffer solution,while the migration time was shortened and the column efficiency was significantly improved in electrophoretic separation of FS in borax buffer solution.The combination of these two nanoparticles with polymers can alter the migration behavior and enhance the separation efficiency and resolution of the analytes,and they are expected to improve the performance of COC microchip electrophoresis as multifunctional additives.